this shows up as top contender in idle cpu usage, because decos in
animations keeps locking weak pointers to shared pointers per window per
frame when its not really needed, use weakpointers all the way and it
drops to a bottom contender. marginal gains in the big picture. but
gains is gains.
moves std::shared_ptrs to a new implementation
Advantages:
- you can dereference a weak_ptr directly. This will obviously segfault on a nullptr deref if it's expired.
- this is useful to avoid the .lock() hell where we are 100% sure the pointer _should_ be valid. (and if it isn't, it should throw.)
- weak_ptrs are still valid while the SP is being destroyed.
- reasoning: while an object (e.g. CWindow) is being destroyed, its `weak_ptr self` should be accessible (the sp is still alive, and so is CWindow), but it's not because by stl it's already expired (to prevent resurrection)
- this impl solves it differently. w_p is expired, but can still be dereferenced and used. Creating `s_p`s is not possible anymore, though.
- this is useful in destructors and callbacks.
